Complex patterns of oscillations in a neural network model with activity-dependent outgrowth
Van Ooyen, A., and Van Pelt, J. (1994). In: Marinaro, M., and Morasso, P. G., eds. Artificial Neural Networks - ICANN 1994, 4th International Conference on Artificial Neural Networks, Sorrento, Italy, pp. 146-149. [Full text: PDF]
Many processes that play a role in shaping the structure of the nervous system are modulated by electrical activity. For example, electrical activity can affect neurite outgrowth: high levels of activity, resulting in high intracellular calcium concentrations, cause neurites to retract, whereas low levels of activity, and consequently low calcium concentrations, allow further outgrowth. As a result of this and other activity-dependent processes, a reciprocal influence exits between the formation of connectivity ('slow dynamics') and activity ('fast dynamics').
We have made a start at unravelling the implications of activitydependent neurite outgrowth, and have been able to show that several interesting properties arise as the result of interactions among outgrowth, excitation and inhibition: (i) a transient overproduction ('overshoot') during development with respect to connectivity; (ii) the neuritic fields of inhibitory cells tend to become smaller than those of excitatory cells; (iii) the spatial distribution of inhibitory cells becomes important in determining the level of inhibition; (iv) pruning of connections can no longer take place if the network has grown without activity for longer than a certain time (’critical period’). The results show many similarities with findings in cultures of dissociated cells.
Previously, we studied networks in which ε, the level of activity for which the neurites of a cell neither grow out nor retract, is the same for all cells. Here, we show that excitatory networks in which ε is distributed over a range of values can display complex patterns of oscillations in electrical activity and outgrowth. Oscillations in neurite outgrowth have indeed been observed in tissue cultures of hippocampal cells (S. B. Kater, personal communication).